Electric lamp having directly heated sheet radiator



April 25, 1967 c. R. WALDRON 3,316,387

ELECTRIC LAMP HAVING DIRECTLY HEATED SHEET RADIATOR Filed Nov. 26, 1963 IN VEN TOR. CECIL R. WALDRON Q BMM /Ai ATTORNEYY United States Patent O 3,316,387 ELECTRIC LAMP HAVING DIRECTLY HEATED SHEET RADIATUR Cecil R. Waldron, Long Beach, Calif., assignor to North American Aviation, Inc. Filed Nov. 26, 1963, Ser. No. 325,977 6 Claims. (Cl. 219-354) This invention relates to .an improved radiant energy source and more particularly to an improved radiant .energy heat lamp that can be used to advantage for testing the physical properties of materials at elevated temperatures.

Because of inherent advantages, including cleanliness of Operation and versatility in the manner of use, yradlant energy heat lamps are widely used as a heating means for testing materials to be used in a high temperature environment on the order of 3000 F. A common type of heat lamp used for this purpose comprises a thin helical ribbon heating element enclosed in a quartz tube. However, the design of such lamps imposes certain limitations on their effectiveness for use as a heating means for high temperature testing, particularly where, as is often the case, it is necessary to subject a material to a high temperature over a prolonged period. Since a quartz tube lamp can generaly be cooled only by heat transfer from the surface of the tube to the air surrounding it, the lamp is susceptible to overheating when used for an extended time, `with the consequence that the tube softens and the ribbon heating element sags. The present invention, however, provides a radiant heat lamp overheating of which is effectively prevented through unique design features that provide for positive cooling of the elements of the lamp.

Another disadvantage of the quartz tube-ribbon element type of heat lamp is that its heating ability is severely limited by the basic design itself. Even when a number of quartz tube lamps are mounted in closely packed rows to provide an increase in the total available radiant energy output, a specimen of a material being heated by the bank of such lamps sees a plurality of comparatively narrow high temperature heating elements each separated by wide zones from which no heat energy is radiated. Consequently, the degree of heat concentration on a specimen that can be attained -by means of a bank of quartz tube lamps is limited. In contrast, a radiant heat lamp constructed in accordance with the principles of the invention utilizes a comparatively wide heating element, which allows the element to operate ata lower temperature for a given desired temperature of a specimen being tested. In general, presently available radiant energy heat lamps also have a comparatively short useful life and do not possess rapid heating rates or lend themselves to a precise control of operating temperature. Furthermore, the fragile construction of conventional heat lamps makes them susceptible to breakage and thus inconvenient to use. All of these disadvantages are obviated by the present invention.

It is therefore an object of the present invention to provide a heat lamp capable of evenly distributing radiant energy over a relatively large area. In a preferred embodiment of the invention which is described in greater detail below, this object is accomplished by means of a heat lamp having a sheet-like heating element or filament 3,316,387 Patented Apr. 25, 1967 in the -form of a thin, flat tungsten sheet electrically connected with two copper electrodes or terminals each of which is provided with internal cooling passages. As utilized herein, the term sheet designates a relatively thin but broad element having a considerable width as cornpared with its length, as distinguished from a ribbon of which the width is quite small compared to its length. The heated sheet and a portion of each of said terminals proximate to said sheet are enclosed within a hermetically sealed chamber having one transparent wall formed of a quartz plate, the terminals supporting the heater sheet so that it is substantially parallel to and slightly spaced from the quartz plate. A second quartz plate is disposed substantially parallel to the exterior surface of the first quartz sheet and is spaced therefrom so as to formy a passage between the plates through which air can be forced to cool the plates when the lamp is in use. A ceramic reflector is positioned between the heater sheet and the wall of said casing opposite the quartz plate wall, and two other ceramic reflectors are positioned along the respective edges of the heater sheet that extend between the terminals, these reilectors serving to concentrate the heat radiation from the sheet in the direction of the transparent quartz plate wall of the casing. The lamp is provided with means for forcing air through the passage between the two quartz plates, means for forcing coolant through the internal passages in each of the electrodes, means for evacuating the casing containing the heater sheet, and means for passing a low voltage-high amperage current through the terminals and heater sheet connected therewith. The described arrangement provides a tubular closed heat reflection assembly having heat reilection wall portions and mutually oppositely disposed wall electrically conductive portions. The assembly has la heat projecting opening at one end that is substantially covered by a sheet heater element having portions in electrical contact with the conductive wall portions.

It is another object of the invention to provide a radiant energy heat lamp including effective cooling means for cooling the structure thereof when the lamp is in use, thereby preventing damage to the lamp from overheating.

It is an additional object of the invention to provide a radiant energy heat lamp of strong and durable construction and capable of distributing heat over a comparatively large area.

It is a further object of the invention to provide a heat lamp having a fast heating rate.

It is still another object of the invention to provide a heat lamp the heat output Iof which is readily and accurately controllable.

These and other objects of the invention will become more readily apparent by consideration of the following description in conjunction with the accompanying drawings wherein:

FIG. 1 is a pictorial view illustrating an embodiment of a heat lamp constructed in accordance with the principles of the invention;

FIG. 2 is a plan view of the embodiment of FIG. l;

FIG. 3 is a section-al view of the embodiment of FIG. 1 taken along Section 3-3 of FIG. 2;

FIG. 4 is a sectional view of the embodiment of FIG. 1 taken along Section 4 4 yof FIG. 2;

FIG. 5 is an enlarged view of a detail; and

FIG. 6 sh-ows a frame member constituting a structural component of the illustrated embodiment.

Throughout the specification and drawings like reference characters refer to like parts.

FIG. 1 shows a radiant energy heat lamp constructed in accordance with the principles of the invention and having a steel cover plate with a central opening 12 defined therein. As illustrated in FIGS. 3 and 4 the cover plate is attached by means of a plurality of bolts 14 and nuts 16 to a. flange 18 extending laterally from, and fixedly attached to, the perimeter of a steel casing, generally designated at 20. A sheet-metal frame member 22, seen in cross-section in both FIGS. 3 and 4 and illustrated in perspective in FIG. 6 has a pair of U-shaped side portions and is interposed between two resilient, heat-resistant gaskets 24, 26, preferably formed of asbestos, that are repectively positioned against, `and are generally coextensive with, the cover plate 10 and flange 18. With reference to FIG. 4, steel spacers 15, held in position by respective ones of the bolts 14, are positioned between the U-shaped portions of the frame member 22 to increase the rigidity of the structure. Again in reference to FIGS. 3 and 4, two quartz plates 28, 30 are positioned against respective `adjacent surfaces of the gaskets 24, 26 and are spaced apart by means of washer-shaped steel spacers 32, held in position by respective ones of the bolts 14, so as to form a passage 34 between the quartz plates which communicates at one end with a plenum chamber 36 and at its opposite end with the atmosphere. The chamber 36 is defined by gasket 24, flange 18 and the frame member 22. A duct 37 formed of a suitable heat resistant material, such as copper, extends through a hole in the flange 18 so as to communicate with the plenum chamber 36. A pump (not shown) can be connected to this duct for forcing air into the plenum chamber and through the passage 34 to the atmosphere. The parallel side walls of the frame member 22 bound the passage on each side thereof,

and the spacers 32 are held in position by respective ones of the bolts 14 which pass through the spacers and holes in the two quartz plates 28, 30.

FIG. 3 shows that the walls of the casing 20 define a chamber 3S of rectangular cross-section adjacent the flange 18 and also form two leg members 40, 40a which define passages, respectively designated 42 and 42a, that communicate at Ione end with chamber 38. Copper terminals or electrodes 44, 44a of rectangular cross-section extend through the leg members 40, a respectively and into chamber 38, each terminal being held in fixed position Within the casing by means of flanges, respectively designated as 46 and 46a, which extend laterally from, and are fixedly attached to, the perimeter of the terminals and which are secured by means of a plurality of bolts 48 and nuts 50 to flanges, respectively designated as 52 and 52a, integrally formed at the lower end of each leg member. Electrically insulating gaskets 54 and 54a are respectively interposed between flanges 46, 52 and 46a, 52a to insulate the terminals from the casing. As illustrated in FIG. 5 a washer 55, formed of an electrically insulating material, is also employed to insulate each bolt 48 from the casing and prevent shorting of the terminals.

As can be seen in FIG. 3, a flat, rectangular tungsten filament or heater sheet 56 extends across the length and breadth of chamber 38 between the electrodes 44, 44a, covering all of the heat projecting opening of the heat reflective assembly. Each of two opposite end portions of the heater sheet is locked in electrically conductive relation against the end of a respective terminal by means of one of the clamp members 58, 58a and a plurality of bolts 6) threadedly engaged in holes in the terminal. The heater sheet is disposed substantially parallel to the quartz plate 30 with its side and end edges substantially coextensive with three ofthe edges of each terminal. An alumina heat reflecting block, generally designated at 62 and having a reflective surface 64 that is spaced from and substantially parallel to the heater sheet 56, is fixedly positioned on the bottom wall 66 of the casing 20 and against adjacent walls of the terminals 44, 44a. Each of two additional alumina heat reflecting blocks 68, 68a abuts the quartz plate 30, the bottom, end and side walls of the casing 20, and sides of terminals 44, 44a and heater sheet 56. When the heat lamp is in use the three heat reflecting blocks concentrate the radiant energy emanating from the heater sheet so that the greatest portion thereof passes out of the chamber 38 through the opening of the heat reflective assembly formed by heat reflecting blocks 62, 68, 68a and terminals 44, 44a and in the direction of the quartz plates 28, 30. If desired, a heat reflecting block (not shown) can also be placed between each of the clamp members 58, 58a and the quartz plate 30 to further concentrate heat flow from the heater sheet.

Again in reference -to FIG. 3, electric cables 70, 70a with respective terminal connectors 72, 72a are connected in electrically conductive relation with respective terminals 44, 44a by means of lbolts 74, 74a and nuts 76, 76a. These cables are connected to a source of electric current (not shown) capable of supplying a low voltage-high amperage current to the terminals and heater sheet S6 interconnected therewith, thereby heating the sheet to incandescence and causing it to emit radiant energy. A duct 78 -is fixed to the casing 2f) so as to ibe in communication with the interior of the casing. A pump (not shown) may be connected with duct 78 to evacuate the casing. As can be seen in FIG. l, the terminals are respectively provided with `inlet tubes 80, 80a and outlet tubes 82, 82a fixedly attached to the end of the terminal and in communication with a continuous passage in each terminal (shown in dotted lines in FIG. 3). The temperature of the electrodes can be controlled by forcing a fluid through these passages.

It is to be understood that the materials used in a heat lamp constructed in accordance with the principles of the invention are not necessarily restricted to those specified in the above description, which is exemplary only. For example, the heater sheet 56 may be formed of any suitable electrically conductive material having a high melting point, including molybdenum and tantalum as well as tungsten and alloys of these metals. Furthermore, the heat reflecting side blocks 62, 68 and 68a may be formed of many materials other than alumina, such as magnesia, for example. In some cases, the heat reflecting side blocks may be replaced with metallic reflecting sheets. The gaskets 24, 26, 54, 54a and 55 likewise can be constructed of a great variety of well-known materials that are heat-resistant and, in the case of gaskets S4, 54a and 55, also electrical insulative.

It should be readily apparent that the above-described embodiment of the invention includes design features which eliminate shortcomings of conventional radiant energy heat lamps. As previously pointed out, the comparatively wide heating element (viz, heater sheet 56) utilized in a heat lamp conforming to the invention, together with the arrangement of heat reflectors (viz., blocks 62, 68 and 68a) for reflecting the radiant energy emitted from the heating element substantially -in a single direction, allows the heat element to operate at a lower temperature for a given temperature to be attained in a test specimen being heated by the lamp. A test specimen placed adjacent the transparent wall of the casing 20 is subjected to radiant energy emanating from an area several times larger than the combined surface area of ribbon filaments in a bank of quartz tube heat lamps. This increase in high temperature area not only directs more heat energy upon a test specimen but also reduces heat flow from the specimen as a result of the fact that the specimen is exposed to a lower percentage of cold area surrounding it. Thus for a given heating element temperature, the temperature of a test specimen heated by a lamp conforming to the invention will be higher than that of a specimen heated by la bank of conventional quartz tube lamps, and, because of the same factors, the heating rate of the described lamp will |be increased over that of conventional heat lamps. The invention also provides effective means for cooling critical portions of a heat lamp so that damage from overheating is prevented. Air can be forced through the duct 37, plenum chamber 36, and passage 34 to maintain the temperature of the two quartz plates 28, 30 below that which 'will cause softening and distortion of the plates. Water can also be forced through the passage in each terminal 44, 44a to maintain a substantially const-ant temperature of the terminals irrespective of the temperature of the heater sheet 56, thereby permitting the temperature of the heater sheet itself to be more precisely controlled by variation in the amount of current passed therethrough.

It was also previously mentioned that a heat lamp constructed in accordance with the principles of the invention overcomes the problems of conventional heat lamps respecting their relatively short useful life and susceptibility to breakage. As will be appreciated through ya study of the above description and accompanying drawings illustrating one embodiment of the invention, the invention provides a strong, durable heat lamp having -a construction that permits convenient replacement of its fragile components (viz., the quartz plates 28, 30) in case they are accidentally broken, whereas when the envelope of a quartz tube heat lamp is broken the entire unit is for all practical purposes destroyed. Useful life of a heat lamp constructed as outlined above is increased over that of conventional heat lamps not only as a result of the use of a heating element considerably more massive than that heretofore employed but also as a result of the fact that the temperature of the element need not be so high as in conventional lamps to effect a given test specimen temperature, thus reducing the likelihood of burn-ing out the heating element. Furthermore, the design disclosed herein provides means for evacuating air from the chamber 38 in which the heater sheet 56 is enclosed so as to reduce deterioration of the sheet which would otherwise result if the sheet were in contact with air while at a high temperature. If preferred, an inert gas, such as argon, -may -be introduced into the chamber 38 to provide a protective atmosphere around the heater sheet.

It will -be recognized lby persons skilled in the art that the electrical input applied across the heater sheet 4will depend upon the heat output of the lamp that is desired. The lamp will operate at low voltage and high current rates, in the order of several volts and up to 1000 amperes, providing temperatures in the range of 1000 F. to 2500 F.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to Ibe taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

What is claimed is:

1. A heat lamp comprising:

a reflective assembly having a first pair of mutually spa-ced heat reflective side walls, a second pair of side walls an lan end wall,

a sheet heater element extending across and substantially covering the space between said first pair of heat reflective side walls and spaced from said end wall,

said second pair of side walls comprising first and second lterminals in contact with said filament,

a casing for holding the wall portions in assembled relation, said casing including a pair of hollow leg portions extending rearwardly therefrom, said terminals extending along said hollow leg portions.

2. A hea-t lamp comprising a heat reflective assembly closed at one end and having a heat projecting opening at the other end, said assembly being formed of a pair of mutualy spaced ceramic heat reflective side wall portions and a ceramic heat reflective end wall portion and including mutually oppositely disposed electrically con? ductive wall portions extending from one of said side wall portions to the other, and a casing for holding the Wall portions in assembled relation,

a sheet heat element extending across and substantially covering all of said heat projecting opening and having oppositely disposed portions in electrical contact with .the electrically conductive wall portions, and

a pair of mutually spaced heat transmitting plates covering said opening and secured to each other and the casing in spaced relation to said filament.

3. A radiant energy heat lamp comprising:

a hermetically sealed casing, said casing having a transparent wall at one end thereof,

a heater sheet disposed within said casing and spaced from the WallsI thereof,

a plurality of ceramic reflectors respectively disposed adjacent and substantially .abutting mutually opposite edges of said heater sheet `to direct radiant energy emanatin-g therefrom toward said transparent wall of said casing,

-a first terminal electrically connected to said heater sheet adjacent an edge thereof,

a second terminal electrically connected to said heater sheet adjacent the edge thereof opposite the edge -to which said first terminal is connected,

each of said terminals having at le-as-t one internal passage formed therein through which a `fluid can be passed to control the temperature of said terminals.

4. A radiant energy heat lamp comprising:

a casing having a transparent w-all at one end thereof, said casing being hermetically sealed to enclose a protective atmosphere,

a transparent plate situated on the exterior side of said transparent wall and spaced therefrom so as to define a passage through which a fluid may be forced to control the temperature of said plate and transparen-t wall,

a peripheral frame member cooperating with said casing for providing a coolant receiving plenum in fluid communication with the passage between said plate and transparent wall,

a heater sheet disposed within said casing and spaced from said transparent wall thereof,

at least two terminals for supplying electric current to said heater sheet at opposite end portions thereof, said terminals each having an axially extending passage therein in communication with the exterior of said casing, and

at least one reflective surface disposed wi-thin said casing to reflect radiant energy emitted from said heater sheet in the direction of said tr-ansparent wall of said casing.

5. A heat lamp comprising:

a casing having first and second pairs of side walls and an end wall with hollow leg portions extending from -the end wall adjacent a first pair of opposite side walls,

a pair of mutually spaced ceramic heat reflective side blocks positioned against the respective walls of the second pair of side walls,

a third ceramic heat reflective end block positioned against the end wall,

a pair of terminals each extending through a respective one of said leg portions and adjacent to but spaced from a respective one of the walls of said first pair of said walls, said terminals extending substantially from one of said side blocks to the other, each terminal having a -fluid coolant conduit formed therein and being lfixed to the casing and electrically insulated therefrom,

a heater sheet having a first pair of mutually opposite edge portions adjacent the side blocks and the second pair of mutually opposite edge portions in electrical contact with and secured to the respective terminals,

a heat transmitting assembly secured to the casing adjacent ends of said side blocks remote from said end block and spaced from said heater sheet, said 'assembly comprising first and second quartz plates and means securing the plates to each other in mutual- 2,784,335 3/ 1957 Munday. ly spa-ced relation and to the casing, said securing 2,896,004 7/ 1959 Duiy et al. 13-25 X means including a peripheral frame member co- 3,059,086 10/ 1962 Pedersen 219-354 X operating with the casing to provide `a coolant re- 3,095,506 6/1963 Dewey et al. 219-553 X ceiving chamber in iiuid communication with the 5 space between the quartz plates. FOREIGN PATENTS 6. A heat lam-p as dened in claim 5 including: means 129,054 8/1950 Sweden for providing a protective atmosphere within said casing.

References by the Examiner 1U Plllml'y Exllml''.

UNITED STATES PATENTS R. F. STAUBLY, Assistant Examiner.

2,577,184 12/1951 Dietrich et yal. 

1. A HEAT LAMP COMPRISING: A REFLECTIVE ASSEMBLY HAVING A FIRST PAIR OF MUTUALLY SPACED HEAT REFLECTIVE SIDE WALLS, A SECOND PAIR OF SIDE WALLS AN END WALL, A SHEET HEATER ELEMENT EXTENDING ACROSS AND SUBSTANTIALLY COVERING THE SPACE BETWEEN SAID FIRST PAIR OF HEAT REFLECTIVE SIDE WALLS AND SPACED FROM SAID END WALL, SAID SECOND PAIR OF SIDE WALLS COMPRISING FIRST AND SECOND TERMINALS IN CONTACT WITH SAID FILAMENT, A CASING FOR HOLDING THE WALL PORTIONS IN ASSEMBLED RELATION, SAID CASING INCLUDING A PAIR OF HOLLOW LEG PORTIONS EXTENDING REARWARDLY THEREFROM, SAID TERMINALS EXTENDING ALONG SAID HOLLOW LEG PORTIONS. 